If you want one to pass down to your kids, look for one with a hexagonal receiver because they are stronger than the round ones. Also get one made before ww2 because they made millions in mass production, so a quality issue might have been overlooked. When looking at one check the crown on the muzzle because it could have been damaged therefore resulting in loss of accuracy. The date that the rifle was made should be on the recevier below the factory symbol. The tula factory would have put a star, the ivhevsk factory will have a hammer and sickle. The different variations are the 1891 which is the very first design made by sergei moisan and leon nagant. Thats how it got its name because both mens designs were used to make it. Then there are the dragoon and cossack varients which I do not know much about. Then there was the 91/30 which is a 1891 moisan with a revised interrupter and magazine. Then the m38 which is a carbine version of the 91/30. It can't have a bayonet attached. Because of this the soviets started to design the m44. It has a non detachable bayonet that folds to the side. It is basicly like a m38 just with the bayonet.
Didn't mean to write a book on this but I felt like sharing some knowledge... oh a round recevier will do fine just a hexagonal lasts longer and is more desirable

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Guns can't decide to kill , it's the people using the gun that decide to pull the trigger